Solid particles, particularly small particles of controllable size and composition, find utility in a variety of industries. Among other advantages, particles of controlled size and composition provide for greater consistency and predictability in handling and use. For example, small particles of controlled size possess favorable flow characteristics and exhibit little variation in interparticle behavior. When such particles are used in conjunction with a chemical process, uniformity in particle size allows the particles to behave consistently, an attribute that is especially advantageous for the pharmaceutical industry, where the particle size can affect the dissolution rate, bioavailability, and overall stability of the agent.
Various approaches for attaining small and uniform particles have been employed. Conventional comminuting techniques such as crushing, grinding, and milling, rely on mechanical forces that introduce the possibility of contamination, destruction of important biological or chemical properties, and variation in particle size. Alternatively, particles of a controlled size may be produced using conventional precipitation/crystallization methods. The methods, however, often require toxic solvents, resulting in wet particles that require drying, and may also produce particles of considerable size variation. In some instances, supercritical fluid technology, such as the rapid expansion of supercritical solutions is employed. Although use of supercritical fluid technology enables the production of relatively small particles of uniform size, such methods rely on nozzles and tubes for delivering their solution. Thus, systems employing supercritical fluid technology are limited in their scope of use. Low frequency, long-wavelength, unfocused acoustic systems have also been used. However, typically in such systems the variation in particle size is high, the processes are time-consuming, and the reproducibility is poor. Accordingly, improved techniques for generating particles using acoustic energy under controlled conditions are needed.